The removal of old wallpaper or other sheet-like material, such as posters or labels, fixed to walls or other surfaces is ordinarily laborious and involves contamination of the surroundings; for example, it is usually necessary to wet old wallpaper thoroughly with water several times before stripping and/or scraping it off from walls. Since many dwellings have floor coverings which are easily damaged by water or by adhesive residues, expensive measures are necessary to protect them while wallpaper is being removed. Moreover, in recent years, wallpaper and other wallfacing material often have a wet-strength finish or a washable coating which substantially prevents their removal with water or greatly increases the difficulty (for example by necessitating the use of solutions which contain wetting agents) of such removal.
Several alternatives for stripping sheet-like material dry from a substrate are:
1. Modification of the wall or a comparable area, to which such materials are to be bonded, on their surface or in bulk, in order to reduce the interaction with an adhesive which is to be applied (for example, using a wax emulsion or waste paper which has been rendered hydrophobic).
2. Use of "multi-ply wallpaper"; that is, sheet-like material which is built up from at least two layers and which can be split between two layers, at least one layer remaining (after splitting) on the surface to which the material had been bonded.
3. Use of sheet-like material which is coated on the back or modified in bulk and which can therefore exert a weaker interaction with an adhesive which is to be applied.
4. Modification of the adhesive by admixing with it substances which reduce its adhesive strength.
Such possibilities are mentioned in the following publications:
German Offenlegungsschrift No. 2,148,423 describes a paper sheet (as base material for strippable wallpaper, strippable poster papers or the like) comprising a pair of paper webs which are joined to one another in an adjacent arrangement by a zone of comparably weak bonding strength over the entire range of their surfaces in mutual contact. To prevent penetration (through the layers) of an adhesive which is to be applied, the paper webs contain resin-based priming coats.
German Offenlegungsschrift No. 2,237,422 concerns a process for manufacturing a strippable base paper for wallpapering. A polyester-fiber nonwoven is incorporated into the aqueous phase of paper stuff as the latter runs into the paper machine. Moreover, the paper may be impregnated with a hydrophobic emulsion, using an additionally-provided sizing press.
The paper, consisting of two fiber layers felted with one another, for wallpaper and posters according to German Patent Specification No. 2,361,996 (=Canadian Patent Specification No. 1,049,714) has a surface which (after the paper has been bonded to a brick or other wall by means of an adhesive) permits the paper to be detached from the bonding by simple stripping. In this paper, one of the fiber layers corresponds to a conventional base paper for wallpaper; the other is a wallpaper base paper in which 40 to 80% by weight of all fibers are polyolefin fibers and which contains from 0.5 to 5%, relative to the weight of all the fibers, of a thermoplastic synthetic or natural material which has been flocculated from an aqueous dispersion.
A process for producing one-sided gumming on sheet-like support webs, particularly wallpaper webs, is carried out (German Auslegeschrift No. 1,921,800) by applying (in addition to the layer of paste or adhesive) a swelling layer (for example a layer of borax or boric acid) in any desired sequence; it is said that the position of a wallpaper manufactured from this support web can easily be corrected after the wallpaper has been hung on the wall.
According to German Offenlegungsschrift No. 2,056,566, an adhesive (for hanging wall coverings which, after hanging and drying, can readily be removed from the carrier surface) contains particles of a hydrophobic material, for example a wax, a salt of a fatty acid, or polyethylene, in addition to conventional adhesive which can be activated with water.
German Offenlegungsschrift No. 2,343,090 describes an adhesive (which can be stirred with water to give a paste) for bonding fibrous cellulose webs, such as wallpapers, to masonry walls. The adhesive contains 10 to 90% by weight of a cellulose ether, starch or starch ether and 90 to 10% by weight of a non-adhesive, finely powdered organic polymer, such as microcrystalline cellulose, polyethylene or a polyolefin oxide. It is said that wallpaper coated with the adhesive and hung on building walls can be removed from the latter quickly and with clean working by simple stripping and without soaking with water.
German Offenlegungsschrift No. 2,615,725 relates to an adhesive for hanging wallpaper, wall coverings and textile coverings on walls, or fixing them to ceilings or floors of a room in a building or the like, which adhesive consists of conventional adhesive and a powder of particles of very small size, which do not dissolve in the adhesive, do not react with the adhesive and only weakly adhere to the latter or not at all; by this means, it is said that the dried adhesive layer can later be split by stripping the wallpaper or covering which has been hung by means of this adhesive. Quartz flour, glass flour, powdered PVC or polyethylene and rubber flour are mentioned as suitable additive powders, and the adhesive layer is said to split along the wallpaper or covering into two thinner layers, one of which should remain adhering to the wallpaper or covering and the other to the substrate. As a supplement to this, German Offenlegungsschrift No. 2,707,570 indicates that adhesives of this type can be applied by the manufacturer of the wallpaper or covering and then need only be reactivated by the user. Alternatively, such wallpaper can be applied together with an additional adhesive.
Prior proposals for providing a sheet-like material which can be stripped dry, however, have the following disadvantages:--When the surface to which the material is to be bonded has been rendered hydrophobic, it is very difficult to reverse this effect since the surface has then become more or less water-repellent; as a result, difficulties also arise during hanging with adhesives which, as a rule, contain water.
The separate application of waste paper before hanging is a laborious additional working step; moreover, it is difficult to remove the waste again.
Modification of the back (that is, the side which is to be bonded) or modification in bulk of sheet-like material which is to be bonded frequently results, on stripping, in leaving an adhesive layer on the substrate; detachment of the back coating also occurs. Since the adhesive power of commercially-available adhesives differs, combination with modified sheet-like material can also lead to inadequate or excessive adhesion.
After stripping one half of a "multi-ply wallpaper", the other half (including the adhesive layer) remains on the wall so that the substrate, to which the material is to be bonded, is gradually completely changed; adhesion problems also arise if several paper layers are present.
The effectiveness of the modified adhesives depends very strongly on the nature of the substrate to which the materials are to be bonded and on the structure of the sheet-like material which is to be bonded; dry strippability is frequently not ensured in practice.